Wireless electronic devices typically handle one or more cellular communication standards, and/or wireless connectivity standards, and/or broadcast standards, each standard being allocated in one or more frequency bands, and the frequency bands being contained within one or more regions of the electromagnetic spectrum.
For that purpose, a typical wireless electronic device must include a radiating system capable of operating in one or more frequency regions with an acceptable radio-electric performance (in terms of, for instance, reflection coefficient, standing wave ratio, impedance bandwidth, gain, efficiency, or radiation pattern). The integration of the radiating system within the wireless electronic device must be effective to ensure that the overall device attains good radio-electric performance (such as for example in terms of radiated power, received power, sensitivity) without being disrupted by electronic components and/or human loading.
The space within the wireless electronic device is usually limited and the radiating system has to be included in the available space. The radiating system is expected to be small to occupy as little space as possible within the device, which then allows devices to be smaller, or for the addition of more specific components and functionalities into the device. It is even more critical in the case in which the wireless device is a multifunctional wireless device, such as the ones described in patent applications U.S. 2014/0253395 and WO2008/009391. The entire disclosures of patent applications U.S. 2014/0253395 and WO2008/009391 are hereby incorporated by reference.
Besides radiofrequency performance, small size and reduced interaction with human body and nearby electronic components, one of the current limitations of the prior art is that generally the antenna system is customized for every particular wireless handheld device model. The mechanical architecture of each device is different and the volume available for the antenna severely depends on the form factor of the wireless device model together with the arrangement of the multiple components embedded into the device (e.g., displays, keyboards, battery, connectors, cameras, flashes, speakers, chipsets, memory devices, etc.). As a result, the antenna within the device is mostly designed ad hoc for every model, resulting in a higher cost and a delayed time to market. In turn, as typically the design and integration of an antenna element for a radiating structure is customized for each wireless device, different form factors or platforms, or a different distribution of the functional blocks of the device will force to redesign the antenna element and its integration inside the device almost from scratch.
A radiating system for a wireless handheld or portable device typically includes a radiating structure comprising an antenna element which operates in combination with a ground plane layer providing a determined radiofrequency performance in one or more frequency regions of the electromagnetic spectrum. Typically, the antenna element has a dimension close to an integer multiple of a quarter of the wavelength at a frequency of operation of the radiating structure, so that the antenna element is at resonance or substantially close to resonance at the frequency of operation, and a radiation mode is excited on the antenna element. Due to given space limitations in the device and the necessity of providing operation in two or more frequency bands that, in some cases, are located in at least two separate frequency regions of the electromagnetic spectrum, the antenna elements usually present complex mechanical designs and considerable dimensions, mainly due to the fact that antenna performance is highly related to the electrical dimensions of the antenna element. Although the radiating structure is usually very efficient at the resonant frequency of the antenna element and maintains a similar performance within a frequency range defined around the resonant frequency (or resonant frequencies), outside the frequency range the efficiency and other relevant antenna parameters deteriorate with an increasing distance to the resonant frequency.
Some techniques for miniaturizing and/or optimizing the multiband behavior of an antenna element have been described in the prior art. However, the radiating structures described therein still rely on exciting a radiation mode on the antenna element for each one of the frequency bands of operation.
Also, those prior-art multiband antennas usually feature a large and complex structure that quite often needs to be customized for every wireless device. For instance J. Ilvonen et al. “Design Strategy for 4G Handset Antennas and a Multiband Hybrid Antennas”, IEEE Transactions APS, April 2014, discloses an antenna element which is still about 50×15 mm, a quite significant footprint for the current needs of modern smartphones.
In this sense, a radiating system such as the one described in the present disclosure not requiring a complex and/or large antenna formed by multiple arms, slots, apertures and/or openings and a complex mechanical design is preferable in order to minimize such undesired external effects and simplify the integration within the wireless device.
Some other attempts have focused on antenna elements not requiring a complex geometry while still providing some degree of miniaturization by using an antenna element not resonant in the one or more frequency ranges of operation of the wireless device.
For example, patent application WO2007/128340 discloses a wireless portable device comprising a non-resonant antenna element for receiving broadcast signals (such as, for instance, DVB-H, DMB, T-DMB or FM). The wireless portable device further comprises a ground plane layer that is used in combination with the antenna element. Although the antenna element has a first resonant frequency above the frequency range of operation of the wireless device, the antenna element is still the main responsible for the radiation process and for the radio-frequency performance of the wireless device. No radiation mode can be substantially excited on the ground plane layer because the ground plane layer is electrically short at the frequencies of operation (i.e., its dimensions are much smaller than the wavelength). For this kind of non-resonant antenna elements, a matching circuitry is added for matching the antenna to a level of SWR in a limited frequency range, which in this particular case can be around SWR≤6.
Commonly-owned patent application WO2008/119699 describes a wireless handheld or portable device comprising a radiating system capable of operating in two frequency regions. The radiating system comprises an antenna element having a resonant frequency outside the two frequency regions, and a ground plane layer. In this wireless device, while the ground plane layer contributes to enhance the electromagnetic performance of the radiating system in the two frequency regions of operation, it is still necessary to excite a radiation mode on the antenna element. In fact, the radiating system relies on the relationship between a resonant frequency of the antenna element and a resonant frequency of the ground plane layer for the radiating system to operate properly in the two frequency regions. Nevertheless, the solution still relies on an antenna element whose size is related to a resonant frequency that is outside of the two frequency regions.
In order to reduce the volume occupied in the wireless handheld or portable device as much as possible, recent trends in handset antenna design are oriented to maximize the contribution of the ground plane to the radiation process by using small non-resonant elements. However, non-resonant elements may require of complex radiofrequency systems. Thus, the challenge of these techniques mainly relies on the complexity (combination of inductors, capacitors, and transmission lines), which is required to satisfy impedance bandwidth and efficiency specifications.
Commonly owned patent applications WO2010/015365 and WO2010/015364 are intended for solving some of the aforementioned drawbacks. Namely, they describe a wireless handheld or portable device comprising a radiating system including a radiating structure and a radiofrequency system. The radiating structure is formed by a ground plane layer presenting suitable dimensions as for supporting at least one efficient radiation mode and at least one radiation booster capable of coupling electromagnetic energy to the ground plane layer. The radiation booster is not resonant in any of the frequency regions of operation and, consequently, a radiofrequency system is used to properly match the radiating structure to the desired frequency bands of operation. More specifically, in WO2010/015364 each radiation booster is intended for providing operation in a particular frequency region. Thus, the radiofrequency system is designed in such a way that the first internal port associated to a first radiation booster is highly isolated from the second internal port associated to a second radiation booster. The radiofrequency system usually comprises a matching network including resonators for each one of the frequency regions of operation and a set of filters for each one of the frequency regions of operation. Thus, the radiofrequency system requires multiple stages and the performance of the radiating systems in terms of efficiency may be affected by the additional losses of the components.
Commonly owned patent applications WO2014/012796 and U.S. 2014/0015730 disclose a concentrated wireless device comprising a radiating system including a radiating structure and a radiofrequency system, such device operates two or more frequency regions of the electromagnetic spectrum. A feature of the radiating system is that the operation in at least two frequency regions is achieved by one radiation booster, or by at least two radiation boosters, or by at least one radiation booster and at least one antenna element, wherein the radiofrequency system modifies the impedance of the radiating structure, providing impedance matching to the radiating system in the at least two frequency regions of operation of the radiating system.
In commonly owned patent application U.S. 2013/0342416 there is disclosed a radiating system that transmits and receives in first and second frequency regions and includes a radiating structure comprising radiation boosters, or a radiation booster and a radiating element, or radiating elements. The radiating system further includes a radiofrequency system including: first and second reactance cancellation elements providing impedances having an imaginary part close to zero for respective frequencies in the first and second frequency regions, and a delay element interconnecting the first and second reactance cancellation elements to provide a difference in phase to produce first and second impedance loops in the first and second frequency regions, respectively, at an external port. The difference in phase provides operation in at least two frequency bands, each one allocated in a different frequency region of the electromagnetic spectrum, and/or increases the number of operating frequency bands in at least one frequency region of the electromagnetic spectrum, and/or increases the number of operating frequency bands in at least two frequency regions of the electromagnetic spectrum.
Commonly owned patent applications WO2014/012842 and U.S. 2014/0015728 disclose very compact, small size and light weight radiation boosters operating in single or in multiple frequency bands. Such radiation boosters are configured to be used in radiating systems that may be embedded into a wireless handheld device. The patent applications further disclose radiation booster structures and their manufacturing methods that enable reducing the cost of both the booster and the entire wireless device embedding the booster inside the device. The entire disclosure of aforementioned application numbers WO2014/012842 and U.S. 2014/0015728 are hereby incorporated by reference.
Commonly owned patent applications U.S. 62/028,494 and EP14178369 disclose a wireless device including at least one slim radiating system having a slim radiating structure and a radio-frequency system. The slim radiating structure includes one or more booster bars. The booster bar is characterized by its slim width and height factors which facilitate its integration within the wireless device and the excitation of a resonant mode in the ground plane layer, and by its location factor that enables to achieve the most favorable radio-frequency performance for the available space to allocate the booster bar. The entire disclosure of aforementioned application numbers U.S. 62/028,494 and EP14178369 are hereby incorporated by reference.
Another technique, as disclosed in U.S. Pat. No. 7,274,340, is based on the use of two coupling elements. According to the description herein, quad-band operation (GSM 1800/1900 and GSM850/900 bands) is provided with two coupling elements: a low-band (LB) coupling element (for the GSM850/900 bands), and a high-band (HB) coupling element (for the GSM1800/1900 bands), where the impedance matching is provided through the addition of two matching circuits, one for the LB coupling element and another one for the HB coupling element. In spite of using non-resonant elements, the size of the element for the low band is significantly large, being 1/9.3 times the free-space wavelength of the lowest frequency for the low frequency band. Due to such size, the low band element would be a resonant element at the high band. Additionally, the operation of this solution is closely linked to the alignment of the maximum E-field intensity of the ground plane and the coupling element. The size of the low band element undesirably contributes to increase the printed circuit board (PCB) space required by the antenna module.
There are already in the market some off-the-shelf antenna booster solutions that cover each cellular band in a wireless device within the 824-2690 MHz frequency range. For instance, Fractus Antennas S. L. offers a solution based in its mXTEND FR01-S4-224 booster product (hereinafter de FA224 booster) as described in its application note (http://www.fractusantennas.com/wp-content/uploads/2016/07/AN_FR01-S4-224_Junior-All-in-One.pdf), available at www.fractusantennas.com. Despite being a compact, off-the-shelf solution, this arrangement still not covers the LTE700 band and below, through a single booster. Covering such a frequency band is difficult as such a low wavelength is long in terms of the size of a typical wireless platform such as a smartphone, and therefore the inherent bandwidth achievable at those frequencies is usually small. Furthermore, this is particularly challenging when one considers the full cellular range from 698 MHz (at the lower edge of LTE700) up to 960 MHz (at the upper edge of GSM900), which features a bandwidth relative to the central frequency above a 30%. Such a broad bandwidth implies a low Q, which a skilled in the art knows it is usually in contradiction with using a small antenna element.
However, making a large antenna element does not necessarily deliver a suitable solution either. When the element is made large to resonate in the low frequency region (698-960 MHz), quite often a high impedance radiation mode is placed within the high frequency region (e.g. 1710-2690 MHz). This high impedance mode is difficult to match, so solving the problem for the low region (to the expense of enlarging the antenna element) makes actually worse the fit in the high frequency region.
In addition, the above available solution based on the FA224 booster includes a significant clearance area around the component, which makes the integration in a highly populated electronic device cumbersome.
There are other booster based solutions available in the market that cover the entire range of cellular bands (e.g. at least from 698 MHz to 2690 MHz), but those require the use of multiple antenna boosters (see for instance the User Manual of the booster FR01-54-250, “CUBE mXTEND™ (FR01-S4-250)—A standard antenna solution for mobile frequency bands” available at www.fractusantennas.com).
Therefore, a wireless device not requiring a large and complex antenna element yet providing suitable radio-frequency performance to operate in a wide range of communication bands within multiple regions of the electromagnetic spectrum including the low LTE bands and below, would be advantageous as it would ease the integration of the radiating structure into the wireless handheld or portable device. The volume freed up by the absence of a large and complex antenna element would enable smaller and/or thinner devices, as slim electronic devices, or even to adopt radically new form factors which are not feasible today due to the presence of an antenna element featured by a considerable volume.